Cui bono?

Who is benefited thereby? To whom is it a gain? The more usual
meaning attached to the words is, What good will it do? For what good
purpose? It was the question of Judge Cassius. (See Cicero: Pro
Milone, 12, sec. 32.)

“Cato, that great and grave philosopher, did commonly demand, when
any new project was propounded unto him, cui bono, what good
will ensue in case the same is effected?” —Fuller: Worthies
(The Design, i.).